The title complex, [Co2(C8H5NO4S)2(C10H8N2)3(H2O)2]·1.3H2O, was synthesized under hydrothermal conditions. The CoII ion is six-coordinated in a slightly distorted octahedral environment resulting from two carboxylate O atoms of two 2-carboxymethylsulfanyl nicotinate (2-CMSN2-) anions, one water molecule and three N atoms of three 4,4'-bipyridine ligands, with one 4,4'-bipyridine ligand situated on a centre of inversion. Two neighboring CoII ions are linked by two anions, giving a dinuclear [Co2(2-CMSN)2] subunit with a CoCo separation of 6.8600 (3) Å. The dinuclear subunits are joined by bridging 4,4'-bipyridine linkers, generating a three-dimensional network structure. Disordered water molecules are situated in the free space of this network. O-HO hydrogen bonding within and between the subunits enhances the stability of the structure.

The construction of coordination polymers has aroused attention due to their
potential applications, fascinating topologies and entanglement motifs (Wang
et al., 2004).

2-Mercaptonanicotinic acid (2-H2MN) is a multifunctional ligand containing
one carboxyl group, one thiol group and a pyridyl N donor atom. Some complexes
based on the 2-MN2- ligand have been previously investigated, e.g. by Sun
et al. (2011). Recently, on the basis of the 2-H2MN ligand, we
have
designed a new multi-carboxylate ligand, 2-carboxymethylsulfanyl nicotinic
acid (2-H2CMSN) to construct novel complexes (Jiang et al.,
2010;
2012). The 2-H2CMSN ligand is interesting because of its potential
versatile coordination behavior, resulting from one rigid and
one flexible carboxyl group. Due to the flexible carboxyl group, it is
favorable for constructing novel network structures. Here we report the
structure of the new title compound,
[Co(2-CMSN)(4,4'-bipy)1.5(H2O)].0.65H2O, (I).

Complex (I) is isostructural to [Ni(2-CMSN)(4,4'-bipy)1.5(H2O)].0.75H2O
(Jiang et al., 2012). The asymmetric unit of (I) contains one
CoII ion, one 2-CMSN2- ligand, one and a half 4,4-bipy molecules
(the other half being completed by inversion symmetry), one coordination
water molecule and disordered lattice water molecules with an overall
occupancy of 0.65. The coordination environment of the CoII ion is
illustrated in Fig. 1. The CoII ion is six-coordinated in a slightly
distorted octahedral CoN3O3 environment: two O atoms originate from one
flexible carboxyl group and one rigid carboxyl group of two symmetry-related
2-CMSN2- ligands, three N atoms from three 4,4'-bipy molecules and one O atom
from the water molecule. Two adjacent CoII ions are linked by two 2-CMSN2-
ligands to give a dinuclear [Co2(2-CMSN)2] subunit with a Co···Co distance
of 6.8600 (3) Å (Fig. 2). The dinuclear [Co2(2-CMSN)2] subunits are
further
bridged by 4,4'-bipy linkers to generate a final three-dimensional structure
(Fig. 2). The disordered water molecules are situated in the free space of the
resulting network. The 4,4'-bipy molecule that is situated on a centre of
inversion is exactly planar, whereas the other has a dihedral angle between
the two pyridyl rings [N2,C9—C13] and [N3, C14—C18] of 33.16 (7)°.

In the crystal, intra- and inter-subunit O—H···O hydrogen bonds (Table 1)
between the coordinating water molecule and carboxylate O atoms enhance the
stability of the structure.
Although the H atom position of the lattice water molecules could not be
located, the O2W···O2 and O3W···S1 contacts of 2.864 (5) Å
and 3.724 (9) Å, respectively, suggest also participation of these molecules
in hydrogen bonding.

A mixture of 2-H2CMSN (0.4 mmol, 0.086 g), CoCl2 (0.4 mmol, 0.095 g) and
4,4'-bipy (0.4 mmol, 0.062 g) in CH3CH2OH (2 ml)/H2O (18 ml) was stirred
for 1 h. The pH value was adjusted to around 6.0 by
sodium carbonate solution in the entire process. Then the mixture was placed
in a 25 ml stainless steel reactor and heated at 383 K for 24 h, and then
cooled to room temperature for 24 h gave red crystals (yield 46%).

The carbon-bound H-atoms were placed in idealized positions [(C—H = 0.93 or
0.97 Å, Uiso(H) = 1.2Ueq(C)]. The coordinating water H-atoms were
located in a different Fourier map and were refined with an O—H distance
restrained to 0.85 (2) Å [Uiso(H) = 1.2Ueq(O)]. The two lattice
water molecules are occupationally disordered (occupancies of 0.4 for OW2
and 0.25 for OW3). No reasonable H positions could be determined from Fourier
maps for these atoms. Therefore the H atoms of OW2 and OW3 were omitted from
refinement, but included in the final chemical formula.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell e.s.d.'s are taken
into account individually in the estimation of e.s.d.'s in distances, angles
and torsion angles; correlations between e.s.d.'s in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s.
planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor
wR and goodness of fit S are based on F2, conventional
R-factors R are based on F, with F set to zero for
negative F2. The threshold expression of F2 >
σ(F2) is used only for calculating R-factors(gt) etc.
and is not relevant to the choice of reflections for refinement.
R-factors based on F2 are statistically about twice as large
as those based on F, and R- factors based on ALL data will be
even larger.